Paging is an important procedure in a mobile communication network. Paging is for instance used in mobility management when searching for a given subscriber within a network coverage area. The reason for the paging may be that a communication transaction, such as a voice call or the delivery of a text message, is to be carried out between the core network of the mobile communication network and a mobile terminal.
Even if the paging mechanisms vary on a detailed level between different mobile communication network standards (such as GSM, UMTS, LTE, D-AMPS, CDMA2000, FOMA or TD-SCDMA), it remains a fact that paging is as essential procedure in a mobile communication network for locating a mobile terminal. Depending on network standard, a mobile terminal may be referred to as mobile station (MS, in GSM), user equipment (UE, in UMTS), etc. In this document, the term mobile terminal will be consistently used in a non-limiting sense without preference to any particular mobile communication network standard.
In recent years, a feature known as Dual SIM Dual Standby (DSDS) has been introduced for certain mobile terminals. DSDS enables a user to insert not only one Subscriber Identity Module (SIM) card in the mobile terminal, but in fact two SIM cards. In effect, this will provide the mobile terminal with two subscriber identities and allow the user to perform voice calls or other communication transactions using any of the two inserted SIMs. At power-on of the mobile terminal, both SIMs will do an IMSI (International Mobile Subscriber Identity) attach, either to the same or to different mobile communication networks. As there are two SIMs available, there will be two unique IMSIs as well. From a network point of view, the mobile terminal is seen as two different terminals. From an end user perspective, DSDS allows the user to replace two different mobile terminals by a single terminal.
Once the two IMSIs have been attached, the user can accept incoming transactions (such as voice or video calls, data transactions, messaging, etc) on either of the SIMs. The user may also initiate outgoing transactions using the SIM of his preference. However, once one of the SIMs is involved in an active connection (referred to as the primary SIM), the other SIM (secondary SIM) cannot be reached from the network.
In this respect, DSDS differs from DSDC (Dual SIM Dual Connectivity) in that the latter is able to have simultaneously ongoing active connections on the different SIMs. However, the expense of this ability is that the radio interface to the mobile communication network(s) needs to be duplicated in a DSDC terminal. This introduces a significant increase in cost, power consumption and apparatus size. Whereas DSDS has advantages in this respect, there are still some problems associated with DSDS.
For instance, when an active connection is ongoing on the primary SIM, no call or other network service can be received on the secondary SIM. From a network point of view, the secondary SIM seems to have disappeared (i.e., cannot be reached). Paging requests to the secondary SIM will not be received, and the user will not be alerted about an incoming call, SMS or another communication transaction, addressed to the secondary SIM.
One attempt to handle this issue for a manufacturer of mobile terminals may be to explicitly warn end-customers that when for instance making a phone call on the primary SIM, one is not available on the secondary SIM. Not being available (i.e., unable to reach) on one SIM may still be unsatisfying to the user, even if the user understands why.
Furthermore, modern mobile terminals often have operating systems/software platforms, like Android, iOS or Linux, which are heavily network-oriented. In several common situations, such mobile terminals will perform background tasks which involve autonomous connections to the network. Examples of such connections are:                Email—Checking periodically if there is new email available,        RSS feeds—Checking for news flash information,        Current weather and financial data—Frequent updates of changing data,        Software and security updates—Most modern operating systems/software platforms have an auto update function.        
Since the above-mentioned network connections occur autonomously, the user typically does not take any action in order to initiate them. While this of course is convenient, it also means that the user therefore is often not aware of when they occur.
In fact, it can be expected that an average user may not even be aware of such background activities being performed in his mobile terminal. While he will notice the results of the updates, he will probably not give any thought as to how they are achieved.
As a consequence, the secondary SIM is often temporarily not reachable without the user being aware of this fact. There is a risk that the user will perceive this as a malfunction of the mobile terminal and act to return the terminal to the store where it was purchased, and/or make a complaint to the network operator about the perceived service levels.
Therefore, there is a need for improvements with respect to these problems.